The skin on their back is pricked -- perhaps 20 to 60 times -- with different allergens, with the body's reactions hopefully revealing the culprits.

For these people, a home allergy test promises an answer without the unpleasant diagnostic test or its expense. Using a $50 test, by pricking their finger and sending their blood to a lab, customers can have themselves tested for 10 of the most common allergens -- which make up 90 percent of allergies, according to the test makers.

But some doctors and advocates say the test is unreliable, and creates risks that may be harmful or even fatal.

"I don't think there is much value personally, because you're just doing tests without taking a history," said Dr. Anne Miranowski, an allergist with The Pediatric Lung Center in Fairfax, Va. "We determine what tests are necessary based on a person's history. We don't indiscriminately test before we see the patient."

"They may decide 'I'm allergic to milk.' Now they're eliminating a healthy source of calcium and protein from their diet ... when in fact they were never allergic to begin with," Miranowski said.

And many of the tests may be simply unnecessary.

"Would you go for cancer screening right now, you and I? What does it mean if you haven't had symptoms of cancer?" said Dr. Leonard Bielory, an allergist with the University of Medicine and Dentistry of New Jersey, and a fellow of the American Academy of Allergy, Asthma and Immunology.

At the same time, tests can show a negative result, leading the person to do something more dangerous.

"Because tests are normal does not mean things are good," Bielory said.

A case in which a food comes up negative but causes anaphylaxis -- a severe, whole-body allergic reaction -- can prove fatal.

That concern is the reason why Gina Clowes, founder of the blog allergymoms.com, said she would advise against these tests and wouldn't use them with her son, Daniel, who has a number of food allergies.

"Allergic symptoms can run the gamut from annoying to life threatening," she said. "If you're having serious symptoms, for me or my children, only a real M.D. would do when diagnosing or treating them."

Cutting Costs or Benefits?

California-based ImmuneTech manufactures MyAllergyTest, which tests for reactions to 10 common allergens. It has been approved for use by the Food and Drug Administration.

"One of the greatest benefits is it makes allergy testing accessible to everyone," said Kathryn Fairchild, president of ImmuneTech. "It's a great opportunity for people to take health care into their own hands."

While doctors' concerns seem to be based on a patient using the test to self-diagnose their allergies, Fairchild said the test should not be used without consulting a physician, and should be able to help patients who could not otherwise afford an allergy test.

"Physicians [are] reticent to send patients to an allergist because the patients may not get to an allergist," Fairchild said.

She also noted that doctors should be consulted once results were obtained.

"Even if you don't come up positive to allergy, there's no guarantee that you don't have allergies," she said. "We know we're not the end of your allergy testing."

But while MyAllergyTest is cheaper than a skin test administered by an allergist, doctors question its reliability and say they would likely retest rather than use its results.

"Some [tests] are more accurate than others, so it's tough to say how cost effective it is," said Miranowski. "If it's not a great assay that they're running, I wouldn't want to pay anything for it."

Most allergists in the United States would not conduct a blood test in the first place, because a skin test is considered the gold standard.

Blood Test May Be Best to Determine Allergies

"The best test ... is the skin test," said Dr. Dan Dalan, an allergist in Fargo, N.D., and a clinical associate professor at the University of North Dakota School of Medicine. "The majority of things you are allergic to will show up on the skin. That's a given."

Fairchild noted, however, that while U.S. physicians tend to use the skin test, the blood test is more common in Europe and elsewhere.

She noted that a blood test is unlikely to be contaminated for allergy testing, even when done at home.

"There's not much that would actually taint the sample," she said.

Even medications they may be taking would not be likely to cause a problem.

"The beauty is patients can continue to take antihistamines even when they're having the blood tested," she said.

The Benefits of Control

While Clowes said she would not use MyAllergyTest, she knows others who do.

"Some of the people in my support group have done this," she said.

The reason, she suspects, is tied to control of a medical condition.

"With chronic conditions you try to do it on your own," she said. "I guess if that works this is OK, but I want someone to help me even decide what to test."

Invariably, some patients who use the test to self-diagnose will make a change that relieves their allergy symptoms.

"The scenario there is if it makes you feel better, God bless you," Bielory said. "In allergy, the placebo effect is 20-30 percent."

He said some people will inevitably test positive for dust mites, cover their mattress and pillows, and feel better.

At the same time, for most who have dust mite allergies, the coverings will not be enough, and they will find themselves growing frustrated, and then they will need further testing.

"Does that really save you the money?" Bielory asked. "What happens to the person who doesn't feel better? It's a whole environmental control process."

And environment may be the problem with a standard home allergy test.

Miranowski said that some of the 10 things tested for aren't present in her area, and many of the problem trees in Virginia aren't tested for, so the test wouldn't help allergy sufferers there.

Random Allergy Tests May Not Help

"Mountain cedar, while that's really big in Texas, you're not going to have that in Massachusetts," she said. "You're testing for 10 random things."

She said she agrees that the placebo effect will likely play a role in many who think the test would help.

"We want to feel better, so if anyone has any problems, they always think something they do is going to make them better," she said.

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